This disclosure relates to improvements in tissue roll-handling clamps normally mounted on lift trucks or other industrial vehicles for clamping and manipulating large cylindrical rolls of tissue, such as soft facial or toilet tissue, soft toweling tissue, or industrial toweling tissue having relatively low densities ranging generally from about 0.0056 to about 0.015 pounds per cubic inch. Such relatively low-density tissue rolls are much softer and more fragile than rolls of denser, tougher and stronger paper used for printing, packaging, construction and the like which are also clamped and manipulated by roll-handling clamps. In particular, the outwardly curved surfaces of the low-density tissue rolls tend to be deformed inwardly, to a much higher degree than is the case with higher density paper rolls, by the opposed roll-engaging clamping surfaces of a roll-handling clamp when being clamped and manipulated in loading, transporting, warehousing and manufacturing environments. Such extreme deformations can cause significant pressure concentrations on the surfaces of the tissue rolls, leading to rupturing of the surfaces with resultant expensive loss of tissue material, and/or radial unbalancing of the tissue rolls rendering them unusable at the desired high rotational speeds of the production equipment with which they are intended to be used.
The foregoing damaging deformations of tissue rolls by roll-handling clamps have been partially reduced in the past by the use of special tissue-handling clamp pads having generally larger clamping areas than the clamp pads used for higher density paper rolls. Such tissue-handling clamp pads usually also have either convexly, or shallowly concavely, curved tissue-engagement clamping surfaces which gradually, rather than abruptly, deform the outward curvature of the tissue roll surfaces over at least a major portion of the clamping surface area during clamping engagement, and/or have peripheral clamping areas which recede gradually outwardly and backwards from a major portion of the clamping surface area. However, the foregoing damaging types of deformations of tissue rolls have persisted despite these attempted solutions because no one has previously attributed the damage to other possible causes, and particularly not to factors involving the relative distribution of the weight of the tissue roll between the opposing tissue-engagement clamping surfaces.
Tissue-handling roll clamps have in the past been of the type having the above-described tissue-engagement clamping surfaces extending unequally, by means of respective elongate clamp arms of unequal lengths, from a frame assembly mountable on a lift truck carriage. The unequal-length clamp arm arrangement has been highly preferred to pick up or deposit tissue rolls supported vertically upon, or horizontally in near proximity to, other surfaces by providing a short arm which can engage one side of the roll in a position extending short of the roll's maximum width, and an opposing long arm which can engage the opposite side of the roll in a position extending preferably beyond the roll's maximum width so as to clamp the roll at least approximately diametrically. This previous arrangement is exemplified by FIG. 1 showing alternative tissue rolls 10 or 12 of different respective diameters A or B, both in a horizontal-axis, or “bilge,” position engaged by a short arm 14 and a long arm 16, each arm having a respective tissue-engagement clamping surface 14a, 16a of the type described above. The clamp arms 14 and 16 are usually pivotally mounted on a frame assembly 22 by respective pivot pins such as 14b and 16b to enable opening and closing of the clamp arms by hydraulic cylinders (not shown), but in some cases the clamp arms have been slidably movable toward and away from each other to enable opening and closing.
If the tissue rolls are also expected to be handled with their axes extending vertically, the frame assembly 22 has been equipped with a worm-driving rotator motor such as 24 which can selectively rotate the frame assembly 22, and thus the clamp arms 14 and 16, about a forwardly-extending axis of rotation 26 to positions where they are spaced horizontally for picking up or depositing a vertically oriented tissue roll 12 as shown in FIG. 2. Or, as a still further alternative, the frame assembly has sometimes been equipped with a forwardly-rotating upender which can selectively pivot the frame assembly 22 forwardly 90 degrees, by extension of hydraulic cylinders such as 28, to permit the clamp arms to pick up or deposit a horizontal paper roll 12 from above as exemplified by FIG. 3. In such case, the rotator 24 has also been usable to rotate the clamp arms and the roll horizontally about the now vertically extending axis 26 shown in FIG. 3.
Unequal-length clamp arm arrangements have encountered certain problems in their attempts to handle tissue rolls because the low-density softness of tissue rolls creates an exceptionally large flat deformation in the bottom of a tissue roll when in the “bilge” position, such deformation being indicated as 25 schematically in FIG. 1A. As the flat deformation 28 of a tissue roll becomes larger, the lower clamp arm 14 must become shorter and the upper clamp arm 16 must become longer in order to clamp the roll 12 substantially diametrically in the “bilge” position as shown schematically in FIG. 1A. This means that the longer upper clamp arm 16 must now reach around the roll further to clamp it on the roll's diameter D. Because of this the upper clamp arm 16 must open significantly further to clear the roll at the “clearance” position 16′ indicated in FIG. 1A when approaching the roll, which limits the diameter of the largest tissue roll which can be engaged by the clamp. Trying to minimize this problem would require difficult simultaneous multi-function maneuvering of the lift truck's mast during the approach to the roll, which would increase the risk of roll damage. Additionally, when the roll is in a vertical position, the longer clamp arm is also more difficult to position so that it reaches around the roll, and this problem is especially severe if it is desired to clamp small diameter rolls, thereby making it difficult for the same clamp to be used to clamp both large diameter and small diameter rolls.
Equal-length clamp arm arrangements have been used in the past, instead of the foregoing unequal-length arm arrangements, for the handling of high-density paper rolls. However such equal-arm arrangements have not previously been used for tissue rolls for various reasons resulting from the low density of tissue rolls. For example, for equal-length clamp arm arrangements, the absence of a lower short arm 14 would make handling of tissue rolls in the horizontal “bilge” configuration, as described above, susceptible to increasing roll damage as the flat deformation 25 of the tissue roll becomes larger. This is because the equal-length lower clamp arm would be required to forcibly insert itself into the area, between the flat deformation 25 of the roll and the supporting floor, to reach a substantially vertically oriented clamping roll diameter between the upper clamping surface and the lower clamping surface of an equal-length clamp arm arrangement. The resultant risk of unacceptable damage caused by such a forcible insertion of the lower clamp arm would be high in the case of a low-density tissue roll.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.